This invention is directed to a process for producing a high quality lubricating oil base stock which includes a hydrocracking operation in which a high boiling hydrocarbon feedstock, e.g., a vacuum gas oil (VGO), is subjected to hydrocracking conditions in the presence of a high silica content zeolite catalyst of the faujasite type, e.g., ultrastable zeolite Y (USY), possessing at least one hydrogenation component, e.g., nickel, tungsten, molybdenum or combinations thereof.
It has, of course, long been recognized that one of the most valuable products of the refining of crude mineral oils is lubricating oil. It is common practice to recover a lubricating oil base stock by extracting undesirable components such as sulfur compounds, oxygenated compounds and aromatics from a straight run distillate fraction employing a selective solvent. However, with the gradual decline in the availability of paraffinic base crudes and a corresponding increase in the proportion of naphthenic and mixed naphthenic and asphaltic base crudes, it is becoming increasingly difficult to meet the demand for lubricating oil base stock simply by solvent extraction methods.
In response to this situation, hydrocracking has been developed as a process for converting a heavy hydrocarbon feedstock, e.g., one boiling above about 343.degree. C. (about 650.degree. F.), to a hydrocrackate product yielding a 650.degree. F.- distillate fraction and a 650.degree. F.+ fraction which, following conventional solvent refining, provides a lube oil base stock. During hydrocracking, aromatics and naphthenes present in the feedstock undergo a variety of reactions such as dealkylation, isomerization, ring opening and cracking, followed by hydrogenation.
Known hydrocracking catalysts comprise an acid cracking component and a hydrogenation component. The acid component can be an amorphous material such as an acidic clay or amorphous silica-alumina or, alternatively, a zeolite. Large pore zeolites such as zeolites X and Y possessing relatively low silica:alumina ratios, e.g., less than about 40:1, have been conventionally used for this purpose because the principal components of the feedstocks (gas oils, coker bottoms, reduced crudes, recycle oils, FCC bottoms) are higher molecular weight hydrocarbons which will not enter the internal pore structure of the smaller pore zeolites and therefore will not undergo conversion. The hydrogenation component may be a noble metal such as platinum or palladium or a non-noble metal such as nickel, molybdenum or tungsten or a combination of these metals.